Local and Downstream Impacts of Contemporary Forest Practices on Sediment Yield

Skaugset A., N. Zègre, A. Simmons, and H. Owens

The hydrological impacts of forest management remains a primary concern to resources managers yet much of our understanding about these effects comes from historic paired watershed studies conducted up to four decades ago. While these early studies play a critical role in the development of current best management practices and forest harvesting practices, results do not necessarily reflect the effects of modern forest harvesting. In this presentation we show results of a study conducted at the decade-long Hinkle Creek Paired Watershed Study that examines the local and downstream impacts of forest harvesting on streamflow. Streamflow was measured at the outlet of six (4 treatment|2 reference) headwater catchments and two (1 treatment|1 reference) 3rd –order watersheds. Regression-based change detection models were developed between reference and treated catchments using mean monthly streamflow, instantaneous maximum peak flow, and storm quick flow. Contemporary forest harvesting practices, defined by the Oregon Forest Practice Rule, were used to clear-cut harvest trees in four experimental headwater catchments, while reference catchments remained untouched. Forest harvesting treatments were initiated in the experimental headwater catchments in 2005 (1st entry) removing trees from 13% to 65% of catchment area following a fifteen to eighteen month calibration period.